Superconducting machines comprising superconducting coils, residing in particular of a high-temperature superconductor material, as excitation windings for generating the magnetic fields in the poles are already known from the prior art. In electric machines of this kind, the superconducting coil must be actively cooled via a cooling device, in particular having at least one cold head. If the temperature of the superconducting coil rises above its operating temperature, the rated excitation current for operating the superconducting machine can no longer be achieved.
When operated in generator mode, such superconducting machines, particularly high-temperature superconductor synchronous machines, are also used as energy sources in a stand-alone power system, e.g. on a ship. Here the problem arises as to how, after a malfunction, e.g. a cooling failure, operation of the power system can basically be maintained to a limited extent or restored, as, particularly after a failure of the cooling of the superconducting coil, heating of the excitation winding occurs, with the result that operation at rated current is no longer possible.
To solve this problem, it has been proposed to provide an emergency power supply, e.g. an additional diesel set, which, prior to the actual desired operation being restored, also provides power over a comparatively long period for auxiliary equipment for cooling the superconducting coil as an excitation winding. Here, however, an additional generator device is required, which is expensive and makes superconducting machines, particularly high-temperature superconductor synchronous machines, a less attractive proposition for generating energy in a stand-alone power system.